Check out dis_admin -h for startup options. In order to connect to the Network Manager you may either start dis_admin with the -cluster option, or choose the button after the startup is complete. Type the hostname or IP-address of the machine running the PCI Express Network Manager.
Only one dis_admin process can connect to the Network Manager at any time. If you should ever need to connect to the Network Manager while another dis_admin process is blocking the connection, you can restart the Network Manager to terminate this connection. Afterwards, you can connect to the Network Manager from your dis_admin process (which needs to be running on a different machine than the other dis_admin process).